R help - Nov 2004 - conv() example in R-exts

Hi

[I'm not sure if this is "intelligible to non-programmers" or not]

R-exts  (section 4.2) gives an example  of the .C() function whose 
third argument is

"as.integer(length(a))",

and urges the user to coerce all the arguments to the correct form 
(on pain of  "hard-to-catch errors"
which I now know to be very appropriate, if understated,  phrasing).

  The length()  function returns an integer, according to the helppage.

So, why does the argument above use as.integer()?



-- 
Robin Hankin
Uncertainty Analyst
Southampton Oceanography Centre
SO14 3ZH
tel +44(0)23-8059-7743
initialDOTsurname at soc.soton.ac.uk (edit in obvious way; spam precaution)

On Mon, 8 Nov 2004, Robin Hankin wrote:
> [I'm not sure if this is "intelligible to non-programmers" or
not]
Not, I suspect:  R-exts is not intended to be.
> R-exts  (section 4.2) gives an example  of the .C() function whose 
> third argument is
> 
> "as.integer(length(a))",
> 
> and urges the user to coerce all the arguments to the correct form 
> (on pain of  "hard-to-catch errors"
> which I now know to be very appropriate, if understated,  phrasing).
> 
>   The length()  function returns an integer, according to the helppage.
> 
> So, why does the argument above use as.integer()?
Because things written on help pages can change.

There *is* a potential issue here, as 64-bit platforms could support
longer vectors than an R integer can represent.  I suspect before too long
we will need a `size' type for lengths.  Already object.size() has been 
changed to return a double, not an integer, since people are created 
objects of more than 2Gb in size.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595